async-retry-ng
v2.0.1
Published
Retrying made simple, easy and async
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async-retry-ng
Retrying made simple, easy, and async.
Usage
// Packages
const retry = require('async-retry-ng')
const fetch = require('node-fetch')
await retry(async bail => {
// if anything throws, we retry
const res = await fetch('https://google.com')
if (403 === res.status) {
// don't retry upon 403
bail(new Error('Unauthorized'))
return
}
const data = await res.text()
return data.substr(0, 500)
}, {
retries: 5
})
API
retry(retrier : Function, opts : Object) => Promise
- The supplied function can be
async
or not. In other words, it can be a function that returns aPromise
or a value. - The supplied function receives two parameters
- A
Function
you can invoke to abort the retrying (bail) - A
Number
identifying the attempt. The absolute first attempt (before any retries) is1
.
- A
- The
opts
retries
: The maximum amount of times to retry the operation. Default is10
.factor
: The exponential factor to use. Default is2
.minTimeout
: The number of milliseconds before starting the first retry. Default is1000
.maxTimeout
: The maximum number of milliseconds between two retries. Default isInfinity
.randomize
: Randomizes the timeouts by multiplying with a factor between1
to2
. Default istrue
.onRetry
: an optionalFunction
that is invoked after a new retry is performed. It's passed theError
that triggered it as a parameter.
All time values are in milliseconds.
Retries Explained
The formula used to calculate the individual timeouts is:
Math.min(random * minTimeout * Math.pow(factor, attempt), maxTimeout)
Have a look at this article for a better explanation of approach.
If you want to tune your factor
/ times
settings to attempt the last retry
after a certain amount of time, you can use wolfram alpha. For example in order
to tune for 10
attempts in 5 minutes
, you can use this equation:
Explaining the various values from left to right:
k = 0 ... 9
: Theretries
value (10)1000
: TheminTimeout
value in ms (1000)x^k
: No need to change this,x
will be your resulting factor5 * 60 * 1000
: The desired total amount of time for retrying in ms (5 minutes)
To make this a little easier for you, use wolfram alpha to do the calculations:
http://www.wolframalpha.com/input/?i=Sum%5B1000*x^k%2C+{k%2C+0%2C+9}%5D+%3D+5+*+60+*+1000